Etching method of multilayered film

ABSTRACT

Verticality of a space formed in the multilayered film can be improved while suppressing an opening of a mask from being clogged. The multilayered film includes a first film and a second film that have different permittivities and are alternately stacked on top of each other. An etching method of etching the multilayered film includes preparing, within a processing vessel of a plasma processing apparatus, a processing target object having the multilayered film and a mask provided on the multilayered film; and etching the multilayered film by exciting a processing gas containing a hydrogen gas, a hydrofluorocarbon gas, a fluorine-containing gas, a hydrocarbon gas, a boron trichloride gas and a nitrogen gas within the processing vessel.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No.2014-162809 filed on Aug. 8, 2014, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The embodiments described herein pertain generally to an etching methodof etching a multilayered film.

BACKGROUND

As a kind of semiconductor device, there is known a NAND type flashmemory device having a three-dimensional structure. In the manufactureof this NAND type flash memory device having the three-dimensionalstructure, a deep hole is formed in a multilayered film, which iscomposed of alternately stacked two layers having differentpermittivities, by performing an etching process. This etching processis described in Patent Document 1.

To elaborate, in Patent Document 1, there is described a method ofetching a multilayered film by exposing a processing target objecthaving a mask on the multilayered film to plasma of a processing gascontaining a HBr gas, a C₄F₈ gas and a BCl₃ gas. In the method describedin Patent Document 1, a polycrystalline silicon film of the multilayeredfilm is etched by an active species generated from the HBr gas; asilicon oxide film of the multilayered film is etched by active speciesgenerated from the C₄F₈ gas; and a protective film generated from theBCl₃ gas is deposited on a sidewall surface formed by the etching of themultilayered film. The protective film suppresses the multilayered filmfrom being etched in a direction (i.e., a horizontal direction)orthogonal to a stacking direction (i.e., a vertical direction) of themultilayered film. Therefore, verticality of a space such as a holeformed in the multilayered film can be improved.

Patent Document 1: International Publication No. 2014/010499

In the etching method described in Patent Document 1, however, the sizeof the opening of the mask may become smaller, and, occasionally, theopening may be completely clogged. Further, it is still required tofurther improve the verticality of the space formed in the multilayeredfilm by forming a stronger protective film.

Thus, in the present technical field, the clogging of the opening of themask needs to be suppressed, and the verticality of the space formed inthe multilayered film needs to be improved.

SUMMARY

In one exemplary embodiment, an etching method of etching a multilayeredfilm is provided. The multilayered film includes a first film and asecond film that have different permittivities and are alternatelystacked on top of each other. The etching method includes preparing,within a processing vessel of a plasma processing apparatus, aprocessing target object having the multilayered film and a maskprovided on the multilayered film; and etching the multilayered film byexciting a processing gas containing a hydrogen gas, a hydrofluorocarbongas, a fluorine-containing gas, a hydrocarbon gas, a boron trichloridegas and a nitrogen gas within the processing vessel.

The processing gas used in this etching method includes a nitrogen gas.Active species generated from the nitrogen gas etches acarbon-containing deposit deposited on the mask, so that an opening ofthe mask is suppressed from being clogged with the deposit. Further, theactive species of the nitrogen gas nitrifies a protective film formed ona sidewall surface forming a space formed in the multilayered film, thatis, a protective film containing boron. As a result, the protective filmis modified to be a stronger protective film. Thus, verticality of thespace formed in the multilayered film can be further improved.

In the exemplary embodiment, the hydrofluorocarbon gas may be a CH₂F₂gas, a CH₃F gas or a CHF₃ gas. The fluorine-containing gas may be a NF₃gas or a SF₆ gas. The hydrocarbon gas may be a CH₄ gas.

In the exemplary embodiment, the first film may be a silicon oxide film,and the second film may be a silicon nitride film. The first film may bea silicon oxide film, and the second film may be a polysilicon film. Thefirst film and the second film may be stacked in twenty-four or morelayers in total.

In the exemplary embodiment, the mask may be made of amorphous carbon.

According to the exemplary embodiment described above, it is possible toimprove verticality of the space formed in the multilayered film whilesuppressing the opening of the mask from being clogged.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description that follows, embodiments are described asillustrations only since various changes and modifications will becomeapparent to those skilled in the art from the following detaileddescription. The use of the same reference numbers in different figuresindicates similar or identical items.

FIG. 1 is a flowchart for describing a method of etching a multilayeredfilm according to an exemplary embodiment;

FIG. 2 is a diagram showing an example wafer prepared in a process ST1;

FIG. 3 is a diagram illustrating an outline of a plasma processingapparatus;

FIG. 4 is a diagram providing a detailed view of a valve group, a flowrate controller group and a gas source group shown in FIG. 3;

FIG. 5 is a diagram showing a wafer being etching in a process ST2;

FIG. 6 is a diagram for describing inclination angles obtained in anexperimental example and a comparative example;

FIG. 7 is a diagram for describing a deviation amounts of a central lineobtained in the experimental example and the comparative example; and

FIG. 8 is a table showing the inclination angles and the deviationamounts obtained in the experimental example and the comparativeexample.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the description. In thedrawings, similar symbols typically identify similar components, unlesscontext dictates otherwise. Furthermore, unless otherwise noted, thedescription of each successive drawing may reference features from oneor more of the previous drawings to provide clearer context and a moresubstantive explanation of the current exemplary embodiment. Still, theexemplary embodiments described in the detailed description, drawings,and claims are not meant to be limiting. Other embodiments may beutilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented herein. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein and illustrated in the drawings, may bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein.

FIG. 1 is a flowchart for describing a method of etching a multilayeredfilm according to an exemplary embodiment. The method MT shown in FIG. 1is applicable to a manufacture of, for example, a NAND flash memoryhaving a three-dimensional structure. The method MT includes a processST1 and a process ST2.

In the process ST1, a processing target object (hereinafter, referred toas “wafer”) is prepared. FIG. 2 is a diagram illustrating an example ofthe wafer W prepared in the process ST1. The wafer W shown in FIG. 2 hasa base layer UL, a multilayered film IL and a mask MSK. The base layerUL may be a polycrystalline silicon layer provided on a substrate. Themultilayered film IL is provided on the base layer UL. The multilayeredfilm IL has a structure in which two dielectric films IL1 and IL2 havingdifferent permittivities are alternately stacked. In the exemplaryembodiment, the dielectric film IL1 may be a silicon oxide film, and thedielectric film IL2 may be a silicon nitride film. In other exemplaryembodiments, the dielectric film IL1 may be a silicon oxide film, andthe dielectric film IL2 may be a polysilicon film. By way ofnon-limiting example, a thickness of the dielectric film IL1 is in therange from, but not limited to 5 nm to 50 nm, and a thickness of thedielectric film IL2 is in the range from, but not limited to, 10 nm to75 nm. The dielectric films IL1 and IL2 may be stacked in twenty-four ormore layers in total. The mask MSK is provided on the multilayered filmIL. The mask MSK has a pattern for forming a space such as a hole in themultilayered film IL. The mask MSK may be made of, by way of example,but not limitation, amorphous carbon. Alternatively, the mask MSK may bemade of, for example, organic polymer.

Referring back to FIG. 1, in the process ST1 of the method MT, the waferW is prepared within a processing vessel of a plasma processingapparatus. As an example, the plasma processing apparatus may beconfigured as a capacitively coupled plasma processing apparatus. Below,an example of the plasma processing apparatus in which the method MT canbe performed will be first explained. FIG. 3 is a diagram depicting anoutline of the plasma processing apparatus and illustrates alongitudinal cross-sectional view of the plasma processing apparatus.

The plasma processing apparatus 10 shown in FIG. 3 is configured as acapacitively coupled plasma etching apparatus and includes asubstantially cylindrical processing vessel 12. An inner wall surface ofthe processing vessel 12 is made of anodically oxidized aluminum. Thisprocessing vessel 12 is frame-grounded.

A substantially cylindrical supporting member 14 is provided on a bottomof the processing vessel 12. Within the processing vessel 12, thesupporting member 14 is vertically extended from the bottom of theprocessing vessel 12. The supporting member 14 sustains a placing tablePD provided within the processing vessel 12. To elaborate, as depictedin FIG. 3, the supporting member 14 may support the placing table PD onan inner wall surface thereof.

The placing table PD is configured to hold the wafer W on a top surfacethereof. The placing table PD may include a lower electrode 16 and asupporting unit 18. The lower electrode 16 is made of a metal such as,but not limited to, aluminum and has a substantially circular plateshape. The supporting unit 18 is provided on a top surface of this lowerelectrode 16.

The supporting unit 18 is configured to support the wafer W and includesa base member 18 a and an electrostatic chuck 18 b. The base member 18 ais made of a metal such as, but not limited to, aluminum and has asubstantially circular plate shape. The base member 18 a is provided onthe lower electrode 16 and is electrically connected with the lowerelectrode 16. The electrostatic chuck 18 b is provided on the basemember 18 a. The electrostatic chuck 18 b has a structure in which anelectrode as a conductive film is embedded between a pair of insulatinglayers or insulating sheets. The electrode of the electrostatic chuck 18b is electrically connected with a DC power supply 22. The electrostaticchuck 18 b is configured to attract and hold the wafer W by anelectrostatic force such as a Coulomb force generated by a DC voltageapplied from the DC power supply 22.

A focus ring FR is provided on a peripheral portion of the base member18 a of the supporting unit 18 to surround a peripheral of the wafer Wand the electrostatic chuck 18 b. The focus ring FR is provided toimprove etching uniformity. The focus ring FR is made of a material thatis appropriately selected depending on a material of an etching targetfilm. By way of non-limiting example, the focus ring FR may be made ofquartz.

A coolant path 24 is formed within the base member 18 a. The coolantpath 24 constitutes a temperature control device according to theexemplary embodiment. A coolant of a preset temperature is supplied intoand circulated through the coolant path 24 from an external chiller unitvia pipelines 26 a and 26 b. By controlling the temperature of thecoolant being circulated, a temperature of the wafer W held on thesupporting unit 18 can also be controlled.

Further, the plasma processing apparatus 10 is also equipped with a gassupply line 28. The gas supply line 28 is configured to supply a heattransfer gas from a heat transfer gas supply unit, for example, a Hegas, to between a top surface of the electrostatic chuck 18 b and a rearsurface of the wafer W.

In addition, the plasma processing apparatus 10 also includes an upperelectrode 30. The upper electrode 30 is provided above the placing tablePD to face the placing table PD. The lower electrode 16 and the upperelectrode 30 are provided to be substantially parallel to each other. Aprocessing space S in which a plasma process is performed on the wafer Wis formed between the upper electrode 30 and the lower electrode 16.

The upper electrode 30 is held at a top portion of the processing vessel12 with an insulating shield member 32 therebetween. The upper electrode30 may include an electrode plate 34 and an electrode supporting body36. The electrode plate 34 confronts the processing space S and isprovided with a multiple number of gas discharge holes 34 a. Theelectrode plate 34 may be made of a low-resistance conductor orsemiconductor having a low Joule heat.

The electrode supporting body 36 is configured to support the electrodeplate 34 in a detachable manner, and may be made of a conductivematerial such as, but not limited to, aluminum. The electrode supportingbody 36 may have a water-cooling structure. A gas diffusion space 36 ais formed within the electrode supporting body 36. A multiple number ofgas through holes 36 b respectively communicating with the gas dischargeholes 34 a is extended downwards from the gas diffusion space 36 a.Further, the electrode supporting body 36 is provided with a gas inletopening 36 c through which a processing gas is introduced into the gasdiffusion space 36 a. The gas inlet opening 36 c is connected with a gassupply line 38.

The gas supply line 38 is connected to a gas source group 40 via a valvegroup 42 and a flow rate controller group 44. FIG. 4 provides a detailedview of the valve group, the flow rate controller group and the gassource group shown in FIG. 3. As depicted in FIG. 4, the gas sourcegroup 40 includes an N number of (N is a natural number) gas sources 401to 406. The gas sources 401 to 406 are sources of a hydrogen gas (H₂gas), a hydrofluorocarbon gas, a fluorine-containing gas, a hydrocarbongas, a boron trichloride (BCI₃) gas and a nitrogen gas (N₂) gas,respectively. As an example of the hydrofluorocarbon gas, a CH₂F₂ gas, aCH₃F gas or a CHF₃ gas may be used. As an example of thefluorine-containing gas, a NF₃ gas or a SF₆ gas may be used. An exampleof the hydrocarbon gas may be CH₄. Further, the gas source group mayfurther include various other gas sources of, for example, a rare gassuch as an Ar gas.

The flow rate controller group 44 includes the N number of flow ratecontrollers 441 to 446. These flow rate controllers 441 to 446 areconfigured to control flow rates of the gases supplied from thecorresponding gas sources. These flow rate controllers 441 to 446 may beimplemented by mass flow controllers (MFC) or FCS. The valve group 42includes the N number of valves 421 to 426. The gas sources 401 to 406are connected to a gas supply line 38 via the flow rate controllers 441to 446 and the valves 421 to 426, respectively. The gases of the gassources 401 to 406 are supplied into the gas diffusion space 36 a viathe gas supply line 38 to be discharged into the processing space Sthrough the gas through holes 36 b and the gas discharge holes 34 a.

Referring back to FIG. 3, the plasma processing apparatus 10 may furtherinclude a grounding conductor 12 a. The grounding conductor 12 a is of asubstantially cylindrical shape and is extended upwards from a sidewallof the processing vessel 12 to a position higher than the upperelectrode 30.

Further, the plasma processing apparatus 10 is also equipped with adeposition shield 46. The deposition shield 46 is detachably providedalong an inner wall of the processing vessel 12. The deposition shield46 is also provided on an outer periphery of the supporting member 14.The deposition shield 46 suppresses an etching byproduct (deposit) fromadhering to the processing vessel 12 and may be made of an aluminummember coated with ceramics such as Y₂O₃.

At a bottom portion of the processing vessel 12, a gas exhaust plate 48is provided between the supporting member 14 and the inner wall of theprocessing vessel 12. The gas exhaust plate 48 may be made of, by way ofexample, but not limitation, an aluminum member coated with ceramicssuch as Y₂O₃. The processing vessel 12 is also provided with an exhaustport 12 e under the gas exhaust plate 38, and the exhaust port 12 e isconnected with a gas exhaust device 50 via a gas exhaust line 52. Thegas exhaust device 50 includes a vacuum pump such as a turbo molecularpump and is capable of depressurizing the inside of the processingvessel 12 to a desired vacuum level. Further, a carry-in/out opening 12g for the wafer W is formed at the sidewall of the processing vessel 12,and this carry-in/out opening 12 g is opened or closed by a gate valve54.

Further, a conductive member (GND block) 56 is provided on the innerwall of the processing vessel 12. The conductive member 56 is fixed tothe inner wall of the processing vessel 12 to be disposed on asubstantially level with the wafer W in a height direction. Thisconductive member 56 is DC-connected to the ground and has an effect ofsuppressing an abnormal discharge. Further, the position of theconductive member 56 may not be limited to the position shown in FIG. 3as long as it is provided within a plasma generation region.

The plasma processing apparatus 10 further includes a first highfrequency power supply 62 and a second high frequency power supply 64.The first high frequency power supply 62 is configured to generate afirst high frequency power for plasma generation of a frequency rangingfrom 27 MHz to 100 MHz. As an example, the first high frequency powersupply 62 generates a high frequency power having a frequency of 40 MHz.The first high frequency power supply 62 is connected to the lowerelectrode 16 via a matching unit 66. The matching unit 66 is a circuitfor matching an output impedance of the first high frequency powersupply 62 with an input impedance on a load side (on the side of thelower electrode 16). The first high frequency power supply 62 may alsobe connected to the upper electrode 30 via a matching unit 66.

The second high frequency power supply 64 is configured to generate asecond high frequency power for ion attraction into the wafer W, i.e., ahigh frequency bias power, of a frequency in the range from 400 kHz to13.56 MHz. As an example, the second high frequency power 64 generates ahigh frequency power of 3 MHz. The second high frequency power supply 64is connected to the lower electrode 16 via a matching unit 68. Thematching unit 68 is a circuit for matching an output impedance of thesecond high frequency power supply 64 with an input impedance on theload side (on the side of the lower electrode 16).

Further, the plasma processing apparatus 10 further includes a DC powersupply unit 70. The DC power supply unit 70 is connected to the upperelectrode 30. The DC power supply unit 70 is configured to generate anegative DC voltage to apply the DC voltage to the upper electrode 30.

Furthermore, in the exemplary embodiment, the plasma processingapparatus 10 may further include a controller Cnt. The controller Cnt isa computer including a processor, a memory, an input device, a displaydevice, and so forth and is configured to control individual componentsof the plasma processing apparatus 10. Through the controller Cnt, anoperator can input commands or the like to manage the plasma processingapparatus 10 by using the input device of the controller Cnt, and anoperational status of the plasma processing apparatus 10 can be visuallydisplayed by the display device. The memory stores therein controlprograms for implementing various processes in the plasma processingapparatus 10 under the control of the processor, or programs forimplementing a process in each component of the plasma processingapparatus 10 according to processing conditions, i.e., processingrecipes.

To elaborate, the controller Cnt outputs control signals to the flowrate controllers 441 to 446, the valves 421 to 426 and the gas exhaustdevice 50 to control them such an etching gas is supplied into theprocessing vessel 12 during an etching process of the process ST2 and,also, an internal pressure of the processing vessel 12 is set to be apredetermined pressure value.

Further, the controller Cnt may also output control signals to the firstand second high frequency power supplies 62 and 64 to supply the highfrequency powers from the first and second high frequency power supplies62 and 64 to the lower electrode 16. In the exemplary embodiment, thecontroller Cnt may output the control signals to the first and secondhigh frequency power supplies 62 and 64 to supply the high frequencypowers to the lower electrode 16 while ON and OFF of the high frequencypowers are switched in a pulse shape. In addition, the controller Cntmay also output a control signal to the DC power supply unit 70 tosupply a negative DC voltage, which has an absolute value larger thanthat of a negative DC voltage applied to the upper electrode 30 during aperiod during which the high frequency powers are ON, to the upperelectrode 30 during a period during which the high frequency powers areOFF. Further, an ON-Off frequency of the high frequency powers from thefirst and second high frequency power supplies 62 and 64 is in the rangeof, but not limited to, 1 kHz to 40 kHz. Here, the “ON-OFF frequency ofthe high frequency powers” refers to a frequency having a single cyclecomposed of an ON period and an OFF period of the high frequency powersof the first and second high frequency power supplies 62 and 64.Further, a duty ratio indicating a ratio of the ON period of the highfrequency powers with respect to the single cycle is, by way of example,but not limitation, in the range from 50% to 90%. Further, thechangeover of the DC voltage of the DC power supply unit may besynchronized with the ON-OFF switchover of the high frequency powersupplies 62 and 64.

Referring back to FIG. 1, the description of the method MT will becontinued. In the process ST1 (Prepare wafer), the wafer W is preparedwithin the processing vessel of the plasma processing apparatus. Whenthe plasma processing apparatus 10 is employed, the wafer W placed onthe placing table PD is attracted to and held on the electrostatic chuck18 b. Subsequently, the process ST2 of the method MT is performed.

In the process ST2 (Etch multilayered film), a multilayered film isetched. For the purpose, the processing gas is supplied into theprocessing vessel of the plasma processing apparatus, and the internalpressure of the processing vessel is set to be a predetermined pressure.In case of using the plasma processing apparatus 10, the processing gasis supplied into the processing vessel 12 from the gas source group 40,and by operating the gas exhaust device 50, the internal pressure of theprocessing vessel 12 can be set to be the predetermined pressure.

The processing gas used in the process ST2 includes a hydrogen gas (H₂gas), a hydrofluorocarbon gas, a fluorine-containing gas, a hydrocarbongas, a boron trichloride (BCl₃) gas and a nitrogen gas (N₂) gas. Anexample of the hydrofluorocarbon gas may be a CH₂F₂ gas, a CH₃F gas or aCHF₃ gas; an example of the fluorine-containing gas, a NF₃ gas or a SF₆gas; and an example of the hydrocarbon gas, CH₄. Further, the processinggas may further include a rare gas such as an Ar gas.

In the process ST2, the processing gas supplied into the processingvessel is excited. In case of using the plasma processing apparatus 10,the high frequency powers from the first and second high frequency powersupplies 62 and 64 are applied to the lower electrode 16.

Various conditions in the process ST2 are as follows.

-   -   Flow rate of H₂ gas: 50 sccm to 300 sccm    -   Flow rate of CH₂F₂: 40 sccm to 80 sccm    -   Flow rate of NF₃: 50 sccm to 100 sccm    -   Flow rate of CH₄: 5 sccm to 50 sccm    -   Flow rate of BCl₃: 5 sccm to 30 sccm    -   Flow rate of N₂ gas: 10 sccm to 200 sccm    -   Frequency of high frequency power of first high frequency power        supply 62: 27 MHz to 100 MHz    -   High frequency power of first high frequency power supply 62:        500 W to 2700 W    -   Frequency of high frequency power of second high frequency power        supply 64: 0.4 MHz to 13 MHZ    -   High frequency power of second high frequency power supply 64:        1000 W to 4000 W    -   Pressure within the processing vessel 12: 2.66 Pa to 13.3 Pa (20        mT to 100 mT)

Further, according to the exemplary embodiment, the ON-OFF switchover ofthe high frequency powers of the first and second high frequency powersupplies 62 and 64 may be performed in a pulse shape. Further,synchronously with the ON-OFF switchover of the high frequency powers ofthe first and second high frequency power supplies 62 and 64, themagnitude of an absolute value of the negative DC voltage applied to theupper electrode 30 may be switched. In the present exemplary embodiment,plasma is generated while the high frequency powers are ON, and theplasma directly above the wafer W is extinguished while the highfrequency powers are OFF. Furthermore, while the high frequency powersare OFF, positive ions are attracted to collide with the upper electrode30 by the negative DC voltage applied to the upper electrode 30.Accordingly, secondary electrons are emitted from the upper electrode30. The emitted secondary electrons modify the mask MSK to improveetching resistance of the mask MSK. Further, the secondary electronsneutralize a charged state of the wafer W. As a result, verticality ofions toward the hole formed in the multilayered film IL is improved.Example conditions regarding the ON-OFF switchover of the high frequencypowers of the first and second high frequency power supplies 62 and 64and conditions for the negative DC voltage applied to the upperelectrode 30 are as follows.

-   -   ON-OFF frequency of high frequency powers: 1 kHz to 40 kHz    -   Duty ratio of ON-period of high frequency powers with respect to        single cycle; 50% to 90%    -   Absolute value of negative DC voltage during ON-period of high        frequency powers: 150 V to 500 V    -   Absolute value of negative DC voltage during OFF-period of high        frequency powers: 350 V to 1000 V

In the process ST2, the processing gas is excited into plasma. Byexposing the wafer W to active species of atoms or molecules containedin the processing gas, the multilayered film IL of the wafer W isetched, as illustrated in FIG. 5. Further, during the etching of theprocess ST2, a deposit DP generated from carbon contained in theprocessing gas is deposited on the mask MSK. The deposit DP may clog theopening of the mask MSK. However, a thickness of the deposit DP isreduced by nitrogen contained in the processing gas. As a result, theopening of the mask MSK is suppressed from being clogged.

Further, during the etching in the process ST2, a compound of boron ofboron trichloride and atoms constituting the multilayered film, e.g.,oxygen and/or nitrogen is generated. As a result, a protective film PFcontaining the corresponding compound is deposited on a sidewall surfaceSW forming a space SP in the multilayered film IL. The protective filmPF may be nitrified by the nitrogen contained in the processing gas.Accordingly, the protective film PF may have more improved resistanceagainst the active species that contributes to the etching of themultilayered film IL. That is, a stronger protective film PF is formed.As a result, the verticality of the space SP formed in the multilayeredfilm IL can be improved.

Further, the processing gas used in the process ST2 contains hydrogen,and the mask MSK is modified by the hydrogen. As a consequence, it ispossible to maintain the shape of the mask until the etching in theprocess ST2 is completed. That is, a mask selectivity against theetching of the multilayered film IL can be improved.

Experimental Examples and Comparative Examples

Below, an experimental example conducted by using the method MT and acomparative example conducted for the comparison will be described.

In the experimental example, the method MT is applied to the wafer Wshown in FIG. 2 by using the plasma processing apparatus 10. Meanwhile,in the comparative example, the multilayered film IL of the wafer Wshown in FIG. 2 is etched by using a processing gas containing an HBrgas instead of the BCI₃ gas without containing the N₂ gas. Further, theother conditions for the etching of the comparative example are the sameas those for the etching of the experimental example.

For each of the wafers W to which the etching of the experimentalexample and the etching of the comparative example are applied,respectively, a cross sectional image of the multilayered film IL inwhich the space is formed by the etching is acquired, and a shape of thespace is observed by using the corresponding cross sectional image. Toelaborate, an inclination angle θ and a center line deviation amount Dof the space SP are obtained. The inclination angle θ is obtained, asshown in FIG. 6, by measuring an angle between a center line Lp and animaginary line Li. Here, the center line Lp refers to a central linebetween a pair of lines Ls that form the space SP, and the imaginaryline Li refers to a line that passes through a center of a top openingof the space SP in a vertical direction. The pair of lines Lscorresponds to sidewall surfaces of the multilayered film IL that formboth sides of the space SP on the cross sectional image. Further, thecenter line deviation amount D is obtained, as illustrated in FIG. 7, bymeasuring distances Ld between the center line Lp and the imaginary lineLi in a horizontal direction at different positions and, then,calculating 3 a of those distances Ld. In addition, the inclinationangle θ and the center line deviation amount D are obtained at a centerposition of the wafer W, an edge position thereof and an intermediateposition between the center position and the edge position in adiametric direction of the wafer W.

FIG. 8 shows the inclination angles θ and the center line deviationamounts D obtained in the experimental example and the comparativeexample. As can be seen from FIG. 8, the inclination angle θ and thecenter line deviation amount D of the space formed in the comparativeexample are found to have fairly large values. The reason why theinclination angle θ and the center line deviation amount D of the spacein the comparative example are so large is because the protection of thesidewall surfaces of the space by the protective film is not sufficientand the sidewall surfaces thereof in the multilayered film arehorizontally etched by ions entering the space in an inclined direction.Further, the reason why the center deviation amount D of the space inthe comparative example is large is also because the opening size of themask is reduced with the lapse of the etching time and a width of thespace is decreased as it goes deep into the multilayered film.Meanwhile, the inclination angle θ and the center line deviation amountD of the space in the experimental example are found to be fairlysmaller than the inclination angle θ and the center line deviationamount D of the space in the comparative example. As can be seen fromthis result, it is found out that by using the processing gas containingBCl₃ gas and N₂ gas instead of HBr gas, the vertically of the space inthe multilayered film can be improved while suppressing the opening sizeof the mask from being reduced.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure. A plasmaprocessing apparatus is not limited to a capacitively coupled plasmaprocessing apparatus. For example, the plasma processing apparatus maybe an inductively coupled plasma processing apparatus or a plasmaprocessing apparatus configured to generate plasma by introducing amicrowave into a processing vessel through a waveguide and an antenna.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims.

We claim:
 1. An etching method of etching a multilayered film includinga first film and a second film that have different permittivities andare alternately stacked on top of each other, the etching methodcomprising: preparing, within a processing vessel of a plasma processingapparatus, a processing target object having the multilayered film and amask provided on the multilayered film; and etching the multilayeredfilm by exciting a processing gas containing a hydrogen gas, ahydrofluorocarbon gas, a fluorine-containing gas, a hydrocarbon gas, aboron trichloride gas and a nitrogen gas within the processing vessel.2. The etching method of claim 1, wherein the hydrofluorocarbon gas is aCH₂F₂ gas, a CH₃F gas or a CHF₃ gas.
 3. The etching method of claim 1,wherein the fluorine-containing gas is a NF₃ gas or a SF₆ gas.
 4. Theetching method of claim 1, wherein the hydrocarbon gas is a CH₄ gas. 5.The etching method of claim 1, wherein the first film is a silicon oxidefilm, and the second film is a silicon nitride film.
 6. The etchingmethod of claim 1, wherein the first film is a silicon oxide film, andthe second film is a polysilicon film.
 7. The etching method of claim 1,wherein the first film and the second film are stacked in twenty-four ormore layers in total.
 8. The etching method of claim 1, wherein the maskis made of amorphous carbon.